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EP3524985B1 - Apparatus and method for insulation monitoring with detection of defective outer conductor in an unearthed 3-phase power supply system - Google Patents

Apparatus and method for insulation monitoring with detection of defective outer conductor in an unearthed 3-phase power supply system Download PDF

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Publication number
EP3524985B1
EP3524985B1 EP19152932.0A EP19152932A EP3524985B1 EP 3524985 B1 EP3524985 B1 EP 3524985B1 EP 19152932 A EP19152932 A EP 19152932A EP 3524985 B1 EP3524985 B1 EP 3524985B1
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Prior art keywords
measuring
outer conductor
voltage
phase
neutral
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German (de)
French (fr)
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EP3524985A1 (en
Inventor
Manfred Geiss
Carsten Weiss
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Bender GmbH and Co KG
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Bender GmbH and Co KG
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/12—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing
    • G01R31/1227—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials
    • G01R31/1263—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials of solid or fluid materials, e.g. insulation films, bulk material; of semiconductors or LV electronic components or parts; of cable, line or wire insulation
    • G01R31/1272—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials of solid or fluid materials, e.g. insulation films, bulk material; of semiconductors or LV electronic components or parts; of cable, line or wire insulation of cable, line or wire insulation, e.g. using partial discharge measurements
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
    • G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
    • G01R27/025—Measuring very high resistances, e.g. isolation resistances, i.e. megohm-meters
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
    • G01R31/52—Testing for short-circuits, leakage current or ground faults
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/40—Testing power supplies
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
    • G01R31/58—Testing of lines, cables or conductors

Definitions

  • the invention relates to a device and a method for insulation monitoring with detection of a faulty outer conductor in a 3-phase ungrounded power supply system, with a first coupling circuit for connecting one of the outer conductors, with a pulse generator for generating a measuring current, with a first measuring device for measuring a Measurement voltage drop caused by the measurement current and with an evaluation device for determining an insulation resistance.
  • the secondary side of the feeding network transformer or the power generating generator has no direct connection to the earth potential - to earth. If a first insulation fault occurs in the electrical system connected to the feed point, such as a ground fault in a connected consumer or in an external conductor itself, no critical fault current initially flows and the system can usually continue to be operated - at least there are no high-energy fault situations. Since the first fault has now resulted in a grounded network, a second insulation fault would have the same serious consequences as in a grounded power supply system (TN system - French: terre neutre). It is therefore necessary to recognize the first error immediately and, depending on the individual risk assessment of the system, to eliminate it promptly or even to switch off the affected system part immediately.
  • TN system - French terre neutre
  • Insulation monitoring devices for isolated power supply systems are for example in ES 2 319 897 T3 , CN 101 915 884 B , US 2016/315461 A1 , US 2015/255976 A1 and in DE 198 37 933 A1 disclosed.
  • insulation monitoring devices are usually used which have a pulse generator that functions as a measurement voltage generator that superimposes a measurement voltage on the network. If an insulation fault occurs, a measuring circuit closes between a faulty outer conductor and earth, in which a measuring current proportional to the insulation fault flows, which is recorded as a measuring voltage drop by means of a measuring device of the insulation monitoring device and is evaluated in an (insulation resistance) evaluation device of the insulation monitoring device in order to determine the insulation resistance determine.
  • an insulation fault location device is used for this purpose.
  • This comprises a test current generator for generating a test current and a (test current) evaluation device with measuring current transformers connected to it in order to localize the faulty line outlet.
  • the insulation monitoring device detects a first insulation fault in the unearthed power supply system
  • the insulation fault location starts with the test current generator generating a test current which is fed into the unearthed power supply system between one or more active conductors and earth.
  • a closed circuit is created in which the test current flows from the test current generator via the live conductor or conductors, the insulation fault and via an earth connection back to the test current generator.
  • the location of the fault is localized by detecting the test current by the measuring current transformer, with a measuring current transformer being permanently assigned to each line section to be monitored.
  • test current is recorded as differential current by all measuring current transformers in the test circuit (fault current circuit), evaluated in the evaluation device and displayed by the insulation fault locator.
  • the fault location can be localized through the known assignment of the measuring current transformers to the line branches.
  • test current generators are very difficult to find on the market, or it is expensive to construct a test current generator designed for such high operating voltages, since the corresponding voltage-resistant components are very are expensive.
  • the insulation strength of the components of the insulation fault location device often represents a problem which can prevent insulation fault location.
  • the retrofitting of existing systems can also be difficult, since the installation space for corresponding, so-called "divisible" current transformers, which can be retrofitted, is usually not available.
  • the use of tape converters is also often undesirable because of the limited accuracy and sensitivity.
  • conventional insulation fault location systems work rather slowly. It can take more than 10 seconds to locate the fault, which is far above the requirements for the above-mentioned applications.
  • the present invention is therefore based on the object of constructing a device and specifying a method which enable insulation monitoring and rapid detection of a faulty outer conductor in a 3-phase ungrounded power supply system, to whose outer conductor each similar consumer is connected.
  • the first measuring device is designed for measuring a line voltage between the connected outer conductor and earth and by a second coupling circuit for connecting a star point and by a second measuring device for Measurement of a neutral point voltage between the neutral point and earth
  • the evaluation device is designed to evaluate a phase position between the mains voltage and the neutral point voltage in order to determine a faulty outer conductor.
  • the basic idea of the present invention is based on the phase angle between the measured mains voltage and the measured one, based on just one measurement of the mains voltage to earth on one of the outer conductors and a measurement of the neutral point voltage to earth To determine the neutral point voltage.
  • the value of the phase angle determined in this way lies in one of three angle ranges that are each assigned to one of the three outer conductors, so that the defective outer conductor is determined.
  • the angular areas each extend over 120 degrees, so that no areas that cannot be assigned remain.
  • the angular ranges assigned to each individual outer conductor can be set for specific applications. On the one hand, this enables adaptation to the individual phase angle of the loads and, on the other hand, the definition of areas that should not be assigned to a single outer conductor (a single phase) (e.g. in the event of insulation faults on two outer conductors). In the latter case, this leads to the entire system being switched off because it is not possible to assign the faulty outer conductor.
  • the faulty outer conductor is thus determined by measuring just one mains voltage in conjunction with measuring the neutral point voltage by evaluating the phase position between the two measured voltages.
  • the first measurement device is therefore designed according to the invention so that it can be used to measure the line voltage between the outer conductor and earth.
  • the neutral point voltage between the neutral point and earth is measured via a second coupling circuit in conjunction with a second measuring device.
  • the evaluation device is designed in such a way that, in addition to determining the insulation resistance, the phase position between the first measuring device measured mains voltage and the neutral point voltage measured by the second measuring device is determined.
  • the phase position determined in this way provides information about which of the outer conductors in the 3-phase ungrounded power supply system is faulty.
  • the two-sided coupling according to the invention with the first and the second coupling circuit enables the faulty outer conductor to be identified in connection with the evaluation of the phase positions of the measured mains voltage and the measured neutral point voltage.
  • the device equipped according to the invention in this way can be regarded as an extended insulation monitoring device which, in addition to monitoring the insulation resistance, offers the possibility of detecting a faulty outer conductor.
  • the evaluation device has a decision maker in order to assign the determined phase position to an external conductor.
  • the decision maker carries out an assignment between the determined phase position and one of the three outer conductors by checking in which of the three angular ranges of the same size and each assigned to one of the outer conductors the determined phase value lies.
  • the device according to the invention has a control output for controlling a separating device for at least one outer conductor.
  • a control output is provided to control the disconnection device.
  • the control output carries a control signal corresponding to the assignment result obtained in the evaluation device.
  • the object on which the invention is based is achieved based on a method in conjunction with the preamble of claim 4 by measuring a line voltage between the connected outer conductor and earth by means of the first measuring device, connecting a star point to a second coupling circuit, measuring a star point voltage between the star point and earth by means of a second measuring device and evaluating a phase position between the mains voltage and the neutral point voltage by means of the evaluation device.
  • the line voltage between the outer conductor and earth is measured by means of the first measuring device.
  • the star point of the 3-phase ungrounded power supply system is also connected via the second coupling circuit in order to also be able to measure the star point voltage between the star point and earth using the second measuring device.
  • the evaluation device also evaluates the phase position between the mains voltage and the neutral point voltage. The phase position is evaluated by deciding in which of the angular ranges assigned to an outer conductor the determined value of the phase position lies.
  • the phase position between the mains voltage and the neutral point voltage is evaluated by measuring a period of the mains voltage, determining a phase shift time between the mains voltage and the neutral point voltage and converting the phase shift time into the phase position with assignment of the faulty outer conductor.
  • the period of the mains voltage is determined. This can be done by detecting the zero crossings of the line voltage curve and a distance determination of the zero crossings take place. In connection with the measurement of the neutral point voltage, a phase shift time between the mains voltage and the neutral point voltage is determined. This phase shift time is then converted into the phase position, taking into account the period duration.
  • outer conductor L1 is faulty if the phase angle is greater than 300 degrees and less than / equal to 60 degrees
  • outer conductor L2 is faulty if the phase angle is greater than 60 degrees and less than / equal to 180 degrees
  • outer conductor L3 is faulty if the phase angle is greater than 180 degrees and less than / equal to 300 degrees.
  • a disconnecting device in the power supply system is activated via a control output, which separates the outer conductor recognized as faulty according to the assignment between phase position and outer conductor and thus the load from the power supply system.
  • a device 2 according to the invention is shown in a 3-phase ungrounded power supply system 4, which comprises the outer conductors L1, L2 and L3, to each of which a consumer 6 is connected.
  • the ungrounded power supply system 4 is provided with a separating device 5 which can switch off each of the outer conductors L1, L2, L3 separately.
  • the device 2 comprises a first coupling circuit 10 for connecting the outer conductor L1, a pulse generator 12 for generating a measuring current, a first measuring device 14 for measuring a measuring voltage drop Um caused by the measuring current and an evaluation device 15 for determining an insulation resistance.
  • the first coupling circuit 10 can be designed with a high resistance, so that advantageously no large powers with high heat generation need to be dissipated there.
  • it is possible to reduce the dielectric strength by using a commercially available voltage converter or by using a low-voltage tap of the IT system transformer that may be present.
  • the first measuring device 14 uses the first coupling circuit 10 to detect the line voltage U between the external conductor L1 and earth PE.
  • the first measuring device 14 thus has circuit components such as, for example, operational amplifier circuits, which are suitable for processing nominal voltages of the ungrounded power supply system.
  • the device 2 further comprises a second coupling circuit 16 for connecting a star point N - or a neutral conductor connected to the star point N - and a second measuring device 18 for measuring a star point voltage Us between the star point N and earth PE.
  • the power dissipation of the second coupling circuit 16 can be viewed as minimal if the measure of immediate disconnection of the outer conductor L3 afflicted with the fault 13 is used.
  • the phase position between the mains voltage U and the neutral point voltage Us is evaluated in order to determine the faulty external conductor L3 via the assignment between the value of the phase position and external conductor L1, L2, L3.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Testing Of Short-Circuits, Discontinuities, Leakage, Or Incorrect Line Connections (AREA)

Description

Die Erfindung betrifft eine Vorrichtung und ein Verfahren für eine Isolationsüberwachung mit Erkennung eines fehlerbehafteten Außenleiters in einem 3-phasigen ungeerdeten Stromversorgungssystem, mit einer ersten Ankopplungsschaltung zum Verbinden von einem der Außenleiter, mit einem Pulsgenerator zur Erzeugung eines Messstroms, mit einer ersten Messeinrichtung zur Messung eines durch den Messstrom bewirkten Messspannungsabfalls und mit einer Auswerteeinrichtung zur Bestimmung eines Isolationswiderstands.The invention relates to a device and a method for insulation monitoring with detection of a faulty outer conductor in a 3-phase ungrounded power supply system, with a first coupling circuit for connecting one of the outer conductors, with a pulse generator for generating a measuring current, with a first measuring device for measuring a Measurement voltage drop caused by the measurement current and with an evaluation device for determining an insulation resistance.

Elektrische Anlagen, mit hohem Leistungsbedarf, wie zum Beispiel Schmelzöfen, Temperöfen, sonstige Erwärmungsvorrichtungen oder Abscheideanlagen der chemischen Industrie benötigen oftmals besondere Schutzmaßnahmen zur Begrenzung der Auswirkungen elektrischer Fehler. Begründet ist dies durch die Notwendigkeit, Brände, Explosionen oder chemische Störfälle zu verhindern. Weiterhin besteht oftmals die Notwendigkeit, elektrische Anlagen bei Auftreten eines elektrischen Fehlers über einen gewissen Zeitraum noch weiter betreiben zu können, um einen Produktionsausfall zu vermeiden oder weil ein Produktionsprozess aus betrieblichen oder physikalischen Gründen nicht kurzfristig unterbrechbar ist.Electrical systems with high power requirements, such as melting furnaces, tempering furnaces, other heating devices or separation systems in the chemical industry often require special protective measures to limit the effects of electrical faults. This is justified by the need to prevent fires, explosions or chemical accidents. Furthermore, there is often the need to be able to continue operating electrical systems for a certain period of time in the event of an electrical fault in order to avoid a loss of production or because a production process cannot be interrupted at short notice for operational or physical reasons.

Idealerweise werden diese Ziele durch Verwendung eines ungeerdeten Stromversorgungssystems zur Stromversorgung erreicht, welches auch als isoliertes Stromversorgungssystem oder kurz als IT-System bezeichnet (frz. Isolé Terre - IT) wird.Ideally, these goals are achieved by using an unearthed power supply system for power supply, which is also referred to as an isolated power supply system or IT system for short (French Isolé Terre - IT).

Bei dieser Netzform weist die Sekundärseite des einspeisenden Netztransformators oder der stromerzeugende Generator keine direkte Verbindung zum Erdpotential - zu Erde - auf. Tritt in der mit der Einspeisestelle verbundenen elektrischen Anlage ein erster Isolationsfehler wie beispielsweise ein Erdschluss in einem angeschlossenen Verbraucher oder an einem Außenleiter selbst auf, so fließt zunächst kein kritischer Fehlerstrom und die Anlage kann meist weiter betrieben werden - zumindest kommt es nicht zu hochenergetischen Fehlersituationen. Da durch den ersten Fehler nunmehr ein geerdetes Netz entstanden ist, hätte ein zweiter Isolationsfehler die gleiche folgenschwere Auswirkung wie in einem geerdeten Stromversorgungssystem (TN-System - frz. terre neutre). Es ist daher erforderlich, den ersten Fehler sofort zu erkennen und diesen, abhängig von der individuellen Gefährdungsbeurteilung der Anlage, zeitnah zu beseitigen oder gar den betroffenen Anlagenteil sofort abzuschalten.With this type of network, the secondary side of the feeding network transformer or the power generating generator has no direct connection to the earth potential - to earth. If a first insulation fault occurs in the electrical system connected to the feed point, such as a ground fault in a connected consumer or in an external conductor itself, no critical fault current initially flows and the system can usually continue to be operated - at least there are no high-energy fault situations. Since the first fault has now resulted in a grounded network, a second insulation fault would have the same serious consequences as in a grounded power supply system (TN system - French: terre neutre). It is therefore necessary to recognize the first error immediately and, depending on the individual risk assessment of the system, to eliminate it promptly or even to switch off the affected system part immediately.

Isolationsüberwachungsvorrichtungen für isolierte Stromversorgungssysteme sind zum Beispiel in ES 2 319 897 T3 , CN 101 915 884 B , US 2016/315461 A1 , US 2015/255976 A1 und in DE 198 37 933 A1 offenbart.Insulation monitoring devices for isolated power supply systems are for example in ES 2 319 897 T3 , CN 101 915 884 B , US 2016/315461 A1 , US 2015/255976 A1 and in DE 198 37 933 A1 disclosed.

Zur Überwachung des Isolationszustandes der Anlage werden üblicherweise Isolationsüberwachungsgeräte eingesetzt, die einen Pulsgenerator in Funktion eines Messspannungsgenerators aufweisen, der dem Netz eine Messspannung überlagert. Bei Auftreten eines Isolationsfehlers schließt sich zwischen einem fehlerbehafteten Außenleiter und Erde ein Messkreis, in dem ein dem Isolationsfehler proportionaler Messstrom fließt, der mittels einer Messeinrichtung des Isolationsüberwachungsgerätes als Messspannungsabfall erfasst und in einer (Isolationswiderstands-)Auswerteeinrichtung des Isolationsüberwachungsgerätes ausgewertet wird, um den Isolationswiderstand zu bestimmen.To monitor the insulation state of the system, insulation monitoring devices are usually used which have a pulse generator that functions as a measurement voltage generator that superimposes a measurement voltage on the network. If an insulation fault occurs, a measuring circuit closes between a faulty outer conductor and earth, in which a measuring current proportional to the insulation fault flows, which is recorded as a measuring voltage drop by means of a measuring device of the insulation monitoring device and is evaluated in an (insulation resistance) evaluation device of the insulation monitoring device in order to determine the insulation resistance determine.

Da bei elektrischen Anlagen mit hohem Leistungsbedarf zur Verringerung der Betriebsströme und damit auch der verwendeten Leiterquerschnitte oftmals hohe Betriebsspannungen angewandt werden, sind für diese Betriebsspannungen ausgelegte Isolationsüberwachungseinrichtungen teuer, beziehungsweise benötigen aufwändige Ankoppelgeräte.As in electrical systems with high power requirements to reduce the operating currents and thus also the conductor cross-sections used If high operating voltages are often used, insulation monitoring devices designed for these operating voltages are expensive or require complex coupling devices.

Als weiterer Nachteil ist es aufgrund der in den Isolationsüberwachungsgeräten angewendeten Messverfahren lediglich möglich, nur ein einziges (aktives) Isolationsüberwachungsgerät pro IT-System einzusetzen, um eine gegenseitige Beeinflussung der Messvorgänge zu vermeiden. Dieses Isolationsüberwachungsgerät überwacht dann den Gesamtisolationswiderstand der Anlage.As a further disadvantage, due to the measurement methods used in the insulation monitoring devices, it is only possible to use only a single (active) insulation monitoring device per IT system in order to avoid mutual influencing of the measurement processes. This insulation monitoring device then monitors the overall insulation resistance of the system.

Zur vorausschauenden Planung von Wartungsmaßnahmen, zur Durchführung von Reparaturarbeiten aufgrund von Isolationsverschlechterungen oder zum selektiven Abschalten von Anlagenteilen - was einen Weiterbetrieb der restlichen Anlage ermöglicht - ist es erforderlich, den Ort des aufgetretenen Isolationsfehlers in der Anlage bestimmen zu können.For predictive planning of maintenance measures, for carrying out repair work due to insulation deterioration or for selective shutdown of system parts - which enables continued operation of the rest of the system - it is necessary to be able to determine the location of the insulation fault in the system.

Hierfür wird dem Stand der Technik gemäß eine Isolationsfehlersucheinrichtung verwendet. Diese umfasst einen Prüfstromgenerator zur Erzeugung eines Prüfstroms und eine (Prüfstrom-)Auswerteeinrichtung mit daran angeschlossenen Messstromwandlern, um den fehlerbehafteten Leitungsabgang zu lokalisieren.According to the prior art, an insulation fault location device is used for this purpose. This comprises a test current generator for generating a test current and a (test current) evaluation device with measuring current transformers connected to it in order to localize the faulty line outlet.

Ist in dem ungeerdeten Stromversorgungssystem ein erster Isolationsfehler von dem Isolationsüberwachungsgerät erkannt worden, startet die Isolationsfehlersuche, indem der Prüfstromgenerator einen Prüfstrom erzeugt, der an zentraler Stelle in das ungeerdete Stromversorgungssystem zwischen einem oder mehreren aktiven Leitern und Erde einspeist wird. Es entsteht ein geschlossener Stromkreis, in dem der Prüfstrom von dem Prüfstromgenerator über den oder die spannungsführenden aktiven Leiter, den Isolationsfehler und über eine Erdverbindung zurück zu dem Prüfstromgenerator fließt.If the insulation monitoring device detects a first insulation fault in the unearthed power supply system, the insulation fault location starts with the test current generator generating a test current which is fed into the unearthed power supply system between one or more active conductors and earth. A closed circuit is created in which the test current flows from the test current generator via the live conductor or conductors, the insulation fault and via an earth connection back to the test current generator.

Die Lokalisierung des Fehlerortes erfolgt über eine Detektion des Prüfstroms durch die Messstromwandler, wobei jedem zu überwachenden Leitungsabschnitt ein Messstromwandler fest zugeordnet ist.The location of the fault is localized by detecting the test current by the measuring current transformer, with a measuring current transformer being permanently assigned to each line section to be monitored.

Der Prüfstrom wird dabei von allen Messstromwandlern, die in dem Prüfstromkreis (Fehlerstromkreis) liegen, als Differenzstrom erfasst, in der Auswerteeinrichtung ausgewertet und von dem Isolationsfehlersuchgerät angezeigt. Durch die bekannte Zuordnung der Messstromwandler zu den Leitungszweigen kann der Fehlerort lokalisiert werden.The test current is recorded as differential current by all measuring current transformers in the test circuit (fault current circuit), evaluated in the evaluation device and displayed by the insulation fault locator. The fault location can be localized through the known assignment of the measuring current transformers to the line branches.

Bei der zuvor beschriebenen Verwendung hoher Netzspannungen in Stromversorgungssystemen, die Verbraucher mit einem hohen Leistungsbedarf versorgen, sind jedoch geeignete Prüfstromgeneratoren auf dem Markt nur sehr schwer verfügbar, beziehungsweise es ist aufwändig, einen für derartig hohe Betriebsspannungen ausgelegten Prüfstromgenerator zu konstruieren, da entsprechende spannungsresistente Bauteile sehr teuer sind.With the above-described use of high mains voltages in power supply systems that supply loads with a high power requirement, however, suitable test current generators are very difficult to find on the market, or it is expensive to construct a test current generator designed for such high operating voltages, since the corresponding voltage-resistant components are very are expensive.

Weiterhin stellt die Isolationsfestigkeit der Komponenten der Isolationsfehlersucheinrichtung, insbesondere der Messstromwandler, oftmals ein Problem dar, welches einer Isolationsfehlersuche entgegenstehen kann. Die Nachrüstung von bestehenden Anlagen kann ebenfalls schwierig sein, da der Bauraum für entsprechende, nachträglich einbaubare sogenannte "teilbare" Stromwandler, meist nicht zur Verfügung steht. Der Einsatz von Bandwandlern ist aufgrund der eingeschränkten Genauigkeit und Empfindlichkeit oft ebenfalls nicht wünschenswert. Zudem arbeiten konventionelle Isolationsfehlersuchsysteme eher langsam. Bis zur Fehlerlokalisierung können mehr als 10 Sekunden vergehen, was weit oberhalb der Anforderungen für die oben genannten Applikationen liegt.Furthermore, the insulation strength of the components of the insulation fault location device, in particular the measuring current transformer, often represents a problem which can prevent insulation fault location. The retrofitting of existing systems can also be difficult, since the installation space for corresponding, so-called "divisible" current transformers, which can be retrofitted, is usually not available. The use of tape converters is also often undesirable because of the limited accuracy and sensitivity. In addition, conventional insulation fault location systems work rather slowly. It can take more than 10 seconds to locate the fault, which is far above the requirements for the above-mentioned applications.

Insbesondere in 3-phasigen IT-Systemen, in denen unabhängig voneinander an jeder Phase, d. h. an jedem Außenleiter jeweils nur ein von den anderen Außenleitern unabhängiger einphasiger Verbraucher mit hohem Leistungsbedarf angeschlossen ist, ist es wünschenswert, im (ersten) Fehlerfall selektiv nur den fehlerbehafteten, von dem Fehler betroffenen, Außenleiter des 3-phasigen IT-Systems zu identifizieren und diesen gegebenenfalls vom Netz zu trennen, aber die übrigen Verbraucher über die nicht fehlerbehafteten Außenleiter weiter zu versorgen.In particular in 3-phase IT systems in which only one single-phase consumer with a high power requirement, independent of the other external conductors, is connected to each phase, i.e. to each outer conductor, it is desirable to use the (first) In the event of a fault, selectively identify only the faulty outer conductor of the 3-phase IT system affected by the fault and, if necessary, disconnect it from the network, but continue to supply the other consumers via the non-faulty outer conductor.

Vorliegend wird davon ausgegangen, dass die an die jeweilige Phase angeschlossenen Verbraucher hinsichtlich ihres Ersatzschaltbildes mit weitgehend identischen Werten modelliert werden können. Z.B. ist eine rein kapazitive Last an einem Außenleiter und eine rein induktive Last an einem anderen Außenleiter im Rahmen der Erfindung nicht zulässig, da diese Konstellation den Phasenwinkel stark beeinflussen würde.In the present case it is assumed that the consumers connected to the respective phase can be modeled with largely identical values with regard to their equivalent circuit diagram. For example, a purely capacitive load on one outer conductor and a purely inductive load on another outer conductor are not permissible within the scope of the invention, since this constellation would strongly influence the phase angle.

Der vorliegenden Erfindung liegt somit die Aufgabe zugrunde, eine Vorrichtung zu konstruieren und ein Verfahren anzugeben, welche eine Isolationsüberwachung und eine schnelle Erkennung eines fehlerbehafteten Außenleiters in einem 3-phasigen ungeerdeten Stromversorgungssystem ermöglichen, an dessen Außenleiter jeweils gleichartige Verbraucher angeschlossen sind.The present invention is therefore based on the object of constructing a device and specifying a method which enable insulation monitoring and rapid detection of a faulty outer conductor in a 3-phase ungrounded power supply system, to whose outer conductor each similar consumer is connected.

Diese Aufgabe wird bezogen auf eine Vorrichtung in Verbindung mit dem Oberbegriff des Anspruchs 1 dadurch gelöst, dass die erste Messeinrichtung für eine Messung einer Netzspannung zwischen dem verbundenen Außenleiter und Erde ausgeführt ist sowie durch eine zweite Ankopplungsschaltung zum Verbinden eines Sternpunktes und durch eine zweite Messeinrichtung zur Messung einer Sternpunktspannung zwischen dem Sternpunkt und Erde sowie dadurch, dass die Auswerteeinrichtung für eine Auswertung einer Phasenlage zwischen der Netzspannung und der Sternpunktspannung ausgeführt ist, um einen fehlerbehafteten Außenleiter zu ermitteln.This object is achieved in relation to a device in connection with the preamble of claim 1 in that the first measuring device is designed for measuring a line voltage between the connected outer conductor and earth and by a second coupling circuit for connecting a star point and by a second measuring device for Measurement of a neutral point voltage between the neutral point and earth, and in that the evaluation device is designed to evaluate a phase position between the mains voltage and the neutral point voltage in order to determine a faulty outer conductor.

Der Grundgedanke der vorliegenden Erfindung beruht darauf, ausgehend von nur einer Messung der Netzspannung gegen Erde an einem der Außenleiter und einer Messung der Sternpunktspannung gegen Erde den Phasenwinkel zwischen der gemessenen Netzspannung und der gemessenen Sternpunktspannung zu bestimmen. Der Wert des so bestimmten Phasenwinkels liegt in einem von drei Winkelbereichen, die jeweils einem der drei Außenleiter zuzuordnen sind, sodass der fehlerbehaftete Außenleiter bestimmt ist. Beispielsweise erstrecken sich im Falle rein ohmscher Verbraucher und näherungsweise gleichen Ableitkapazitäten der Außenleiter die Winkelbereiche über jeweils 120 Grad, sodass keine nicht zuordenbare Bereiche verbleiben.The basic idea of the present invention is based on the phase angle between the measured mains voltage and the measured one, based on just one measurement of the mains voltage to earth on one of the outer conductors and a measurement of the neutral point voltage to earth To determine the neutral point voltage. The value of the phase angle determined in this way lies in one of three angle ranges that are each assigned to one of the three outer conductors, so that the defective outer conductor is determined. For example, in the case of purely ohmic loads and approximately the same discharge capacities of the outer conductors, the angular areas each extend over 120 degrees, so that no areas that cannot be assigned remain.

Grundsätzlich sind die jedem einzelnen Außenleiter zugeordneten Winkelbereiche applikationsspezifisch einstellbar. Das ermöglicht einerseits die Anpassung an individuelle Phasenwinkel der Verbraucher und andererseits die Definition von Bereichen, die nicht einem einzelnen Außenleiter (einer einzelnen Phase) zugeordnet sein sollen (z. B. bei Isolationsfehlern an zwei Außenleitern). In letzterem Fall führt das zur Abschaltung der gesamten Anlage, weil die Zuordnung des fehlerbehafteten Außenleiters nicht möglich ist.In principle, the angular ranges assigned to each individual outer conductor can be set for specific applications. On the one hand, this enables adaptation to the individual phase angle of the loads and, on the other hand, the definition of areas that should not be assigned to a single outer conductor (a single phase) (e.g. in the event of insulation faults on two outer conductors). In the latter case, this leads to the entire system being switched off because it is not possible to assign the faulty outer conductor.

Die Ermittlung des fehlerbehafteten Außenleiters erfolgt somit durch Messung von nur einer Netzspannung in Verbindung mit der Messung der Sternpunktspannung durch Auswertung der Phasenlage zwischen beiden gemessenen Spannungen.The faulty outer conductor is thus determined by measuring just one mains voltage in conjunction with measuring the neutral point voltage by evaluating the phase position between the two measured voltages.

In Erweiterung der aus dem Stand der Technik bekannten Messung eines durch den Messstrom bewirkten Messspannungsabfalls ist die erste Messeinrichtung daher erfindungsgemäß so ausgeführt, dass mit ihr die Messung der Netzspannung zwischen dem Außenleiter und Erde vorgenommen werden kann.As an extension of the measurement known from the prior art of a measurement voltage drop caused by the measurement current, the first measurement device is therefore designed according to the invention so that it can be used to measure the line voltage between the outer conductor and earth.

Über eine zweite Ankopplungsschaltung wird in Verbindung mit einer zweiten Messeinrichtung erfindungsgemäß die Sternpunktspannung zwischen dem Sternpunkt und Erde gemessen.According to the invention, the neutral point voltage between the neutral point and earth is measured via a second coupling circuit in conjunction with a second measuring device.

Die Auswerteeinrichtung ist so ausgeführt, dass neben der Bestimmung des Isolationswiderstands auch die Phasenlage zwischen der von der ersten Messeinrichtung gemessenen Netzspannung und der von der zweiten Messeinrichtung gemessenen Sternpunktspannung bestimmt wird. Die so ermittelte Phasenlage liefert eine Aussage darüber, welcher der Außenleiter in dem 3-phasigen ungeerdeten Stromversorgungssystem fehlerbehaftet ist.The evaluation device is designed in such a way that, in addition to determining the insulation resistance, the phase position between the first measuring device measured mains voltage and the neutral point voltage measured by the second measuring device is determined. The phase position determined in this way provides information about which of the outer conductors in the 3-phase ungrounded power supply system is faulty.

Die erfindungsgemäße, zweiseitige Ankopplung mit der ersten und der zweiten Ankopplungsschaltung ermöglicht in Verbindung mit der Auswertung der Phasenlagen der gemessenen Netzspannung und der gemessenen Sternpunktspannung den fehlerbehafteten Außenleiter zu erkennen. Die in dieser Weise erfindungsgemäß ausgestattete Vorrichtung kann als ein erweitertes Isolationsüberwachungsgerät aufgefasst werden, welches über die Überwachung des Isolationswiderstands hinaus die Möglichkeit der Erkennung eines fehlerbehafteten Außenleiters bietet.The two-sided coupling according to the invention with the first and the second coupling circuit enables the faulty outer conductor to be identified in connection with the evaluation of the phase positions of the measured mains voltage and the measured neutral point voltage. The device equipped according to the invention in this way can be regarded as an extended insulation monitoring device which, in addition to monitoring the insulation resistance, offers the possibility of detecting a faulty outer conductor.

In weiterer Ausgestaltung weist die Auswerteeinrichtung einen Entscheider auf, um die ermittelte Phasenlage einem Außenleiter zuzuordnen.In a further embodiment, the evaluation device has a decision maker in order to assign the determined phase position to an external conductor.

Der Entscheider führt eine Zuordnung zwischen der ermittelten Phasenlage und einem der drei Außenleiter durch, indem geprüft wird, in welchem der drei gleichgroßen und jeweils einem der Außenleiter zugeordneten Winkelbereiche der ermittelte Phasenwert liegt.The decision maker carries out an assignment between the determined phase position and one of the three outer conductors by checking in which of the three angular ranges of the same size and each assigned to one of the outer conductors the determined phase value lies.

Weiterhin weist die erfindungsgemäße Vorrichtung einen Steuerausgang zur Ansteuerung einer Trennvorrichtung für mindestens einen Außenleiter auf.Furthermore, the device according to the invention has a control output for controlling a separating device for at least one outer conductor.

Um nach Erkennung des fehlerbehafteten Außenleiters den an diesen Außenleiter angeschlossenen Verbraucher vom dem Stromversorgungsnetz trennen zu können, ist zur Ansteuerung der Trennvorrichtung ein Steuerausgang vorgesehen. Der Steuerausgang führt ein Steuersignal entsprechend des in der Auswerteeinrichtung erzielten Zuordnungsergebnisses.In order to be able to disconnect the consumer connected to this external conductor from the power supply network after the faulty external conductor has been detected, a control output is provided to control the disconnection device. The control output carries a control signal corresponding to the assignment result obtained in the evaluation device.

Die der Erfindung zugrundeliegende Aufgabe wird bezogen auf ein Verfahren in Verbindung mit dem Oberbegriff des Anspruchs 4 gelöst durch Messen einer Netzspannung zwischen dem verbundenen Außenleiter und Erde mittels der ersten Messeinrichtung, Verbinden eines Sternpunktes mit einer zweiten Ankopplungsschaltung, Messen einer Sternpunktspannung zwischen dem Sternpunkt und Erde mittels einer zweiten Messeinrichtung und Auswerten einer Phasenlage zwischen der Netzspannung und der Sternpunktspannung mittels der Auswerteeinrichtung.The object on which the invention is based is achieved based on a method in conjunction with the preamble of claim 4 by measuring a line voltage between the connected outer conductor and earth by means of the first measuring device, connecting a star point to a second coupling circuit, measuring a star point voltage between the star point and earth by means of a second measuring device and evaluating a phase position between the mains voltage and the neutral point voltage by means of the evaluation device.

Erfindungsgemäß erfolgt eine Messung der Netzspannung zwischen dem Außenleiter und Erde mittels der ersten Messeinrichtung. Über die zweite Ankopplungsschaltung wird weiterhin der Sternpunkt des 3-phasigen ungeerdeten Stromversorgungssystems angeschlossen, um zusätzlich die Sternpunktspannung zwischen dem Sternpunkt und Erde mittels der zweiten Messeinrichtung messen zu können. In der Auswerteeinrichtung erfolgt über das Bestimmen des Isolationswiderstands hinaus das Auswerten der Phasenlage zwischen der Netzspannung und der Sternpunktspannung. Das Auswerten der Phasenlage erfolgt durch Entscheiden in welchem der jeweils einem Außenleiter zugeordneten Winkelbereiche der ermittelte Wert der Phasenlage liegt.According to the invention, the line voltage between the outer conductor and earth is measured by means of the first measuring device. The star point of the 3-phase ungrounded power supply system is also connected via the second coupling circuit in order to also be able to measure the star point voltage between the star point and earth using the second measuring device. In addition to determining the insulation resistance, the evaluation device also evaluates the phase position between the mains voltage and the neutral point voltage. The phase position is evaluated by deciding in which of the angular ranges assigned to an outer conductor the determined value of the phase position lies.

Somit kann aus der Phasenlage unmittelbar auf den fehlerbehafteten Außenleiter in dem 3-phasigen ungeerdeten Stromversorgungssystem geschlossen werden.In this way, conclusions can be drawn directly from the phase position about the faulty outer conductor in the 3-phase ungrounded power supply system.

In weiterer Ausgestaltung des Verfahrens erfolgt das Auswerten der Phasenlage zwischen der Netzspannung und der Sternpunktspannung durch Messen einer Periodendauer der Netzspannung, Ermitteln einer Phasenverschiebungszeit zwischen der Netzspannung und der Sternpunktspannung und Umrechnen der Phasenverschiebungszeit in die Phasenlage mit Zuordnen des fehlerbehafteten Außenleiters.In a further embodiment of the method, the phase position between the mains voltage and the neutral point voltage is evaluated by measuring a period of the mains voltage, determining a phase shift time between the mains voltage and the neutral point voltage and converting the phase shift time into the phase position with assignment of the faulty outer conductor.

Zunächst wird die Periodendauer der Netzspannung ermittelt. Dies kann durch Detektieren der Nulldurchgänge des Netzspannungsverlaufs und einer Abstandsbestimmung der Nulldurchgänge erfolgen. In Verbindung mit der Messung der Sternpunktspannung wird dann eine Phasenverschiebungszeit zwischen der Netzspannung und der Sternpunktspannung ermittelt. Anschließend wird diese Phasenverschiebungszeit unter Berücksichtigung der Periodendauer in die Phasenlage umgerechnet. Die Zuordnung der Phasenlage zu dem fehlerbehafteten Außenleiter ergibt sich exemplarisch für rein ohmsche Verbraucher und näherungsweise gleichen Ableitkapazitäten der Außenleiter dabei wie folgt: Außenleiter L1 ist fehlerbehaftet, falls der Phasenwinkel größer 300 Grad und kleiner/gleich 60 Grad ist, Außenleiter L2 ist fehlerbehaftet, falls der Phasenwinkel größer 60 Grad und kleiner/gleich 180 Grad ist und Außenleiter L3 ist fehlerbehaftet, falls der Phasenwinkel größer 180 Grad und kleiner/gleich 300 Grad ist.First, the period of the mains voltage is determined. This can be done by detecting the zero crossings of the line voltage curve and a distance determination of the zero crossings take place. In connection with the measurement of the neutral point voltage, a phase shift time between the mains voltage and the neutral point voltage is determined. This phase shift time is then converted into the phase position, taking into account the period duration. The assignment of the phase position to the faulty outer conductor arises as an example for purely ohmic loads and approximately the same discharge capacities of the outer conductors as follows: outer conductor L1 is faulty if the phase angle is greater than 300 degrees and less than / equal to 60 degrees, outer conductor L2 is faulty if the phase angle is greater than 60 degrees and less than / equal to 180 degrees and outer conductor L3 is faulty if the phase angle is greater than 180 degrees and less than / equal to 300 degrees.

Weiterhin wird ein Steuersignal zum Trennen des fehlerbehafteten Außenleiters erzeugt.Furthermore, a control signal for disconnecting the faulty outer conductor is generated.

Ist ein fehlerbehafteter Außenleiter erkannt, so wird über einen Steuerausgang eine in dem Stromversorgungssystem vorhandene Trennvorrichtung angesteuert, welche den gemäß der Zuordnung zwischen Phasenlage und Außenleiter als fehlerbehaftet erkannten Außenleiter und damit die Last von dem Stromversorgungssystem trennt.If a faulty outer conductor is detected, a disconnecting device in the power supply system is activated via a control output, which separates the outer conductor recognized as faulty according to the assignment between phase position and outer conductor and thus the load from the power supply system.

Weitere vorteilhafte Ausgestaltungsmerkmale ergeben sich aus der nachfolgenden Beschreibung und der Zeichnung, die eine bevorzugte Ausführungsform der Erfindung an Hand eines Beispiels erläutert. Es zeigt die

Fig.:
eine erfindungsgemäße Vorrichtung für eine Isolationsüberwachung mit Erkennung eines fehlerbehafteten Außenleiters in einem 3-phasigen ungeerdeten Stromversorgungssystem.
Further advantageous design features emerge from the following description and the drawing, which explains a preferred embodiment of the invention using an example. It shows the
Fig .:
a device according to the invention for insulation monitoring with recognition of a faulty outer conductor in a 3-phase ungrounded power supply system.

In der Fig. ist eine erfindungsgemäße Vorrichtung 2 in einem 3-phasigen ungeerdeten Stromversorgungssystem 4 dargestellt, welches die Außenleiter L1, L2 und L3 umfasst, an die jeweils ein Verbraucher 6 angeschlossen ist. An dem an den Außenleiter L3 angeschlossenen Verbraucher 6 liegt ein Isolationsfehler 13 in Form eines Erdschlusses vor.In the figure , a device 2 according to the invention is shown in a 3-phase ungrounded power supply system 4, which comprises the outer conductors L1, L2 and L3, to each of which a consumer 6 is connected. There is an insulation fault 13 in the form of a ground fault on the consumer 6 connected to the external conductor L3.

Das ungeerdete Stromversorgungssystem 4 ist mit einer Trennvorrichtung 5 versehen, welche jeden der Außenleiter L1, L2, L3 separat abschalten kann.The ungrounded power supply system 4 is provided with a separating device 5 which can switch off each of the outer conductors L1, L2, L3 separately.

Die erfindungsgemäße Vorrichtung 2 umfasst eine erste Ankopplungsschaltung 10 zum Verbinden des Außenleiters L1, einen Pulsgenerator 12 zur Erzeugung eines Messstroms, eine erste Messeinrichtung 14 zur Messung eines durch den Messstrom bewirkten Messspannungsabfalls Um und eine Auswerteeinrichtung 15 zur Bestimmung eines Isolationswiderstands.The device 2 according to the invention comprises a first coupling circuit 10 for connecting the outer conductor L1, a pulse generator 12 for generating a measuring current, a first measuring device 14 for measuring a measuring voltage drop Um caused by the measuring current and an evaluation device 15 for determining an insulation resistance.

Die erste Ankopplungsschaltung 10 kann hochohmig ausgeführt sein, sodass dort vorteilhafterweise keine großen Leistungen mit hoher Wärmeentwicklung abgeführt werden müssen. Zudem ist eine Verringerung der Spannungsfestigkeit durch Verwendung eines handelsüblichen Spannungswandlers oder durch Verwendung eines möglicherweise vorhandenen Niederspannungsabgriffs des IT-Systemtrafos möglich.The first coupling circuit 10 can be designed with a high resistance, so that advantageously no large powers with high heat generation need to be dissipated there. In addition, it is possible to reduce the dielectric strength by using a commercially available voltage converter or by using a low-voltage tap of the IT system transformer that may be present.

Die erste Messeinrichtung 14 erfasst über die erste Ankopplungsschaltung 10 neben dem durch den Messstrom bewirkten Messspannungsabfall Um erfindungsgemäß auch die Netzspannung U zwischen dem Außenleiter L1 und Erde PE.In addition to the measurement voltage drop Um caused by the measurement current, the first measuring device 14 also uses the first coupling circuit 10 to detect the line voltage U between the external conductor L1 and earth PE.

Die erste Messeinrichtung 14 weist somit schaltungstechnische Bauelemente wie beispielsweise Operationsverstärker-Schaltungen auf, die für die Verarbeitung von Nennspannungen des ungeerdeten Stromversorgungssystems geeignet sind.The first measuring device 14 thus has circuit components such as, for example, operational amplifier circuits, which are suitable for processing nominal voltages of the ungrounded power supply system.

Weiterhin umfasst die erfindungsgemäße Vorrichtung 2 eine zweite Ankopplungsschaltung 16 zum Verbinden eines Sternpunktes N - oder eines mit dem Sternpunkt N verbundenen Neutralleiters - und eine zweite Messeinrichtung 18 zur Messung einer Sternpunktspannung Us zwischen dem Sternpunkt N und Erde PE.The device 2 according to the invention further comprises a second coupling circuit 16 for connecting a star point N - or a neutral conductor connected to the star point N - and a second measuring device 18 for measuring a star point voltage Us between the star point N and earth PE.

Auch über die zweite Ankopplungsschaltung 16 an den Sternpunkt N bzw. den Neutralleiter muss im Normalbetrieb keine hohe Leistung abgeführt werden, da der Sternpunkt N im fehlerfreien Zustand annähernd Erdpotential aufweist. Aber auch im Fehlerfall kann die Leistungsabführung der zweiten Ankopplungsschaltung 16 als minimal betrachtet werden, wenn die Maßnahme der sofortigen Abschaltung des mit dem Fehler 13 behafteten Außenleiters L3 angewendet wird.In normal operation, too, no high power needs to be dissipated via the second coupling circuit 16 to the star point N or the neutral conductor, since the star point N has approximately ground potential in the fault-free state. However, even in the event of a fault, the power dissipation of the second coupling circuit 16 can be viewed as minimal if the measure of immediate disconnection of the outer conductor L3 afflicted with the fault 13 is used.

In der Auswerteeinrichtung 15 wird neben der Bestimmung des Isolationswiderstands die Phasenlage zwischen der Netzspannung U und der Sternpunktspannung Us ausgewertet, um über die Zuordnung zwischen Wert der Phasenlage und Außenleiter L1, L2, L3 den fehlerbehafteten Außenleiter L3 zu bestimmen.In the evaluation device 15, in addition to determining the insulation resistance, the phase position between the mains voltage U and the neutral point voltage Us is evaluated in order to determine the faulty external conductor L3 via the assignment between the value of the phase position and external conductor L1, L2, L3.

Die Zuordnung zwischen dem Wert der Phasenlage und den Außenleitern L1, L2, L3 erfolgt in einem Entscheider 22 der Auswerteeinrichtung 15, die Ansteuerung der Trennvorrichtung 5 erfolgt über einen Steuerausgang 24 der Auswerteeinrichtung 15.The assignment between the value of the phase position and the outer conductors L1, L2, L3 takes place in a decision maker 22 of the evaluation device 15, the control of the separating device 5 takes place via a control output 24 of the evaluation device 15.

Für den Anwender des erfindungsgemäßen, erweiterten Isolationsüberwachungsgerätes ergibt sich der Vorteil, dass die Verbraucher (Produktionseinrichtungen) an den nicht von dem Isolationsfehler betroffenen Außenleitern (Phasen), vorliegend L1 und L2 weiter betrieben werden können und so der Produktionsausfall auf die abgeschaltete, fehlerbehaftete Produktionsanlage begrenzt bleibt.For the user of the extended insulation monitoring device according to the invention, there is the advantage that the consumers (production facilities) on the outer conductors (phases) not affected by the insulation fault, in this case L1 and L2, can continue to operate, thus limiting the production downtime to the switched-off, faulty production plant remains.

Claims (6)

  1. A device for insulation monitoring (2) including identification of a faulty outer conductor (L1, L2, L3) in a three-phase ungrounded power supply system (4), comprising a first coupling circuit (10) for connecting one of the outer conductors (L1, L2, L3), comprising a pulse generator (12) for generating a measuring current, comprising a first measuring device (14) for measuring a measuring-voltage drop (Um) effected by the measuring current, and comprising an evaluation device (15) for determining an insulation resistance (Rf),
    characterized in that
    the first measuring device (14) is configured for measuring a mains voltage (U) between the connected outer conductor (L1, L2, L3) and ground (PE) and characterized by a second coupling circuit (16) for connecting a neutral point (N) and by a second measuring device (18) for measuring a neutral-point voltage (Us) between the neutral point (N) and ground (PE) and characterized in that the evaluation device (15) is configured for evaluating a phase between the mains voltage (U) and the neutral-point voltage (Us) for detecting a faulty outer conductor (L1, L2, L3).
  2. The device according to claim 1,
    characterized in that
    the evaluation device (15) comprises an decider (22) for assigning the determined phase to an outer conductor (L1, L2, L3).
  3. The device according to claim 1 or 2,
    characterized by
    a control output (24) for controlling a disconnect device for at least one outer conductor (L1, L2, L3).
  4. A method for insulation monitoring including identification of a faulty outer conductor (L1, L2, L3) in three-phase ungrounded power supply systems, having the method steps:
    - connecting an outer conductor (L1, L2, L3) to a first coupling circuit (10),
    - generating a measuring current by means of a pulse generator (12),
    - measuring a measuring voltage, which is effected by the measuring current, by means of a first measuring device (14),
    - determining an insulation resistance by means of an evaluation device (15),
    characterized by
    - measuring a mains voltage (U) between the connected outer conductor (L1, L2, L3) and ground (PE) by means of the first measuring device (14),
    - connecting a neutral point (N) to a second coupling circuit (16),
    - measuring a neutral-point voltage (Us) between the neutral point (N) and ground (PE) by means of a second measuring device (18), and
    - evaluating a phase between the mains voltage (U) and the neutral point voltage (Us) by means of the evaluation device (15).
  5. The method according to claim 4,
    characterized in that
    the phase between the mains voltage (U) and the neutral-point voltage (Us) is evaluated by measuring a period duration of the mains voltage (U), by determining a phase shift time between the mains voltage (U) and the neutral-point voltage (Us) and by converting the phase shift time to the phase including assigning the faulty outer conductor (L1, L2, L3).
  6. The method according to claim 4 or 5,
    characterized in that
    a control signal for disconnecting the faulty outer conductor (L1, L2, L3) is generated.
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